1. Field of the Invention
This invention relates to a device for detecting an angle displacement by utilizing the force of inertia.
2. Description of the Related Art
The operating principle of the device of the above-stated kind is described below with reference to FIGS. 2 and 3 which show an embodiment of this invention and also to FIG. 15 which shows the fundamental arrangement of an angle displacement detector:
A base 1 is arranged to have various component parts mounted thereon. A tubular casing 2 has a chamber formed within the casing 2 to have a floating body 3 and a liquid 4 sealed therein. As shown in detail in FIG. 3, the tubular casing 2 is provided with a groove part 2a which is formed inside the casing 2 to have a U-shaped floating-body carrier 14 fitted in and secured to the casing 2. The floating-body carrier 14 is arranged to carry the floating body 3 in a state freely rotatable around an axis 3a. A mirror 9 and a mask 10 which covers the mirror 9 and which is provided with a slit 10a are mounted on each of two opposite sides of a center block of the floating body 3. Other opposite sides of the center block have arm parts extending therefrom. The floating body 3 has a magnetic property and has its rotation around the axis 3a and buoyancy within the liquid 4 balanced respectively.
A light emitting element (IRED) 5 is arranged to emit light when energized and is securely mounted on the base 1 by means of a light-emitting-element carrier 7. A light receiving element (PSD) 6 is a photo-electric conversion element which is arranged to vary its output according to the position of light received and is securely mounted on the base 1 by a light-receiving-element carrier 8. These light emitting and receiving elements 5 and 6 form an optical angle-displacement detecting means which transmits light via the mirror 9 mounted on the surface of the center block of the above-mentioned floating body 3. The light-emitting-element carrier 7 is provided with a light guiding part 7a which is arranged to guide the light emitted from the light emitting element 5. To the fore end of the light guiding part 7a is attached a mask 10' which is provided with a slit 10a' in the same manner as the mask 10 which covers the mirror 9 of the above-mentioned floating body 3. The light transmission is effected via the tubular casing 2. Therefore, either the whole of or an applicable part of the tubular casing 2 is arranged to be transparent.
A pair of yokes 19 and 20 are arranged to bring forth a magnetic field acting in such a way as to keep the floating body 3 which has a magnetic property in a given position as shown in FIG. 15. The ends of these yokes are oppositely spaced in the diametral direction of the tubular casing 2 as shown in FIG. 15. Another yoke 21 is interposed in between other ends of the yokes 19 and 20. The yoke 21 is provided with a permanent magnet 22 which is fitted on the yoke 21. A magnetic circuit is formed by the yokes 19, 20 and 21 in conjunction with the floating body 3. The floating body 3 is kept in a posture as shown in FIG. 15 by virtue of a weak magnetic force of the permanent magnet 22.
The floating body 3 is rotatably carried in the following manner: As shown in FIG. 2, a rotation shaft 11 vertically pierces through the center block of the floating body 3. A pivot 12 is press-fitted into each of the upper and lower ends of the rotation shaft 11 with its sharply pointed tip set outward. Meanwhile, the above-mentioned U-shaped floating-body carrier 14 is provided with pivot bearings 13 which are formed in the ends of upper and lower arms in a state of being inwardly opposed to each other. The floating body 3 is carried with the sharp pointed tips of the pivots 12 fitted into these pivot bearings 13 respectively.
An upper lid 15 is attached to the tubular casing 2 to seal the latter in a known manner with a silicon adhesive or the like. A rubber gasket 16 is interposed in between a retainer plate 17 and the upper lid 15 and is fixed in position by means of screws or the like.
With the device arranged in the manner described above, the floating body 3 never has any moment of rotation resulting from the influence of gravity in any posture thereof. Further, to prevent any substantial load on the pivot shaft, the rotation around the axis 3a and the buoyancy in the liquid 4 are arranged to be balanced as mentioned in the foregoing.
In the above-stated arrangement, the inside of the liquid 4 is prevented by inertia from being moved even when the tubular casing 2 rotates around the rotation axis 3a. Therefore, the floating body 3 which is in a floating state never rotates. As a result, the tubular casing 2 and the floating body 3 rotate relative to each other around the rotation axis 3a. This is the operating principle of the device for detecting relative angle displacements. These relative angle displacements are detectable by means of the optical detection means which uses the above-stated light emitting and receiving elements 5 and 6.
In actuality, there arises some flow within the sealed-in liquid 4 due to the influence of the wall surface of the tubular casing 2. The flow then would somewhat act on the floating body 3. However, the adverse effect of this can be minimized by adjusting a distance from the wall surface to the floating body 3, the viscosity of the liquid 4, etc. The device which is arranged in the above stated manner detects an angle displacement as follows:
The light emitted from the light emitting element 5 passes through the light guiding part 7a and is projected onto the floating body 3. The light is then reflected by the mirror 9 to reach the light receiving element 6. Meanwhile, as mentioned in the foregoing, The slits 10a' and 10a of the masks 10' and 10 provided on the fore end of the light guiding part 7a and on the mirror 9 of the floating body 3 cause the light to become approximately parallel light to form an image (of the slit) without any blur on the light receiving element 6.
Since the tubular casing 2 and the light emitting and receiving elements 5 and 6 are fixed to the base 1, they move together with each other. In the event of occurrence of a relative angle displacement between the tubular casing 2 and the floating body 3, the image of the slit on the light receiving element 6 moves to an extent as much as the displacement. As a result, the output of the light receiving element 6, i.e., the photo-electric conversion element, which changes its output according to the position of the light received, becomes proportional to the change in the position of the slit image. The angle displacement of the tubular casing 2 thus can be detected on the basis of the output of the element 6.
With the angle displacement detection device arranged as described above, the floating body 3 is in a state of not receiving any external force. The posture of the floating body 3 thus cannot be controlled. Therefore, under this condition, it would be hardly possible to ensure that the position of the slit image is always within the measuring range of the light receiving element 6 if the device is left in this state. However, the device is provided with the above-stated permanent magnet 22 which causes a weak magnetic field to act on the floating body 3. The action of the magnetic field serves to keep the floating body 3 in a predetermined position as shown in FIG. 15.
In order to enable the angle displacement detector to accurately measure the angle displacement, the floating body 3 must be well balanced around the axis of rotation within the sealed-in liquid 4; and, in addition to that, the floating body 3 also must be well balanced with its buoyancy to impose no substantial load on the bearing parts in the direction of axis of rotation. It is relatively easy to attain the former, i.e., the balance around the rotation axis by selecting the shape of the floating body 3, etc. However, the latter balance, i.e., the balance in the direction of axis of rotation, is dependent upon a relation between the specific gravity of the floating body 3 and that of the liquid 4. Besides, in cases where a magnetic property is imparted to the floating body 3 as in this case, the material used for forming the floating body 3 must be selected from among a limited range of materials and this limitation makes the sealed-in liquid 4 not readily selectable.
In view of this problem, it is conceivable to lessen the apparent specific gravity of the floating body 3 by providing an air chamber within the floating body 3. However, this method not only causes an increase in size of the floating body 3 but also results in an increase in the number of parts for sealing the air chamber part. The increased number of parts then lowers the reliability of the device.
Further, the action of the magnetic field exerts an urging force on the floating body 3. The urging force is exerted in principle to keep the floating body 3 in a given posture or position relative to the tubular casing 2. In other words, it is exerted to have the floating body 3 move in one unified body with the tubular casing 2. Therefore, if the acting force of the magnetic field is too strong, it would move the tubular casing 2 together with the floating body 3 to prevent the relative displacement which is to be used for the angle displacement detection. Whereas, if the acting force of the magnetic field is sufficiently small relative to the inertia of the liquid 4, the device can be arranged to be capable of responding to a relatively low frequency or a relatively slow angle displacement.
The above-stated arrangement to fix the position of the floating body 3 with the above-stated weak acting force of the magnetic field presents no problem in cases where the object the angle of displacement of which is to be measured by the detector normally remains stationary. However, if the object to be measured is intended to be normally carried around or moved, as in the case of a photographic camera, binoculars, or the like, the device is constantly subjected to vibrations. Under such a condition, some irregular flow arises in the sealed-in liquid 4. Then, if the measuring action of the device begins with the sealed-in liquid 4 still having the irregular flow, the output of the light receiving element 6 would vary because of the irregular flow while the object being measured is not actually moving. Under such a condition, therefore, it is hardly possible to make accurate measurement. Besides, in an extreme case, the slit image would be moved to the outside of the measurable range of the light receiving element 6. Under such a condition, therefore, the device must be kept still until the irregular flow of the liquid 4 disappears. In this instance, the small urging force of the weak magnetic field action on the floating body 3 requires a long period of time before the floating body 3 settles down.
Apart from the method of using the weak magnetic field action of the permanent magnet, it is conceivable to use an electromagnet. For example, a current is allowed to flow in a larger quantity to quickly set the floating body 3 in the given position and then the current is lessened to give the small urging force before the start of a measuring action. However, this method increases electric energy consumption to an excessive degree for practicable device as the limited electric energy would be consumed with the current allowed to flow when the device is not actually in use.